The distortion in electric signals is a problem that is felt in several applications. A typical example regards the magneto-resistive read heads, which are typically used in hard disk mass-storage systems.
In such storage systems, data is saved onto a magnetic disk by means of several magnetization statuses of corresponding cells. The reading of such data is performed by means of read heads, which are transducer devices capable of generating a corresponding analog voltage signal transduced from the magnetic field corresponding to the different magnetization statuses. The modern read heads that are used in the hard disk mass-storage systems are based on the magneto-resistive technology. Said heads are made by means of a material that modifies its electric resistance in presence of a magnetic field. A typical hard disk mass-storage system further includes a circuit adapted to interpret the reading signal provided by the read head, and to generate a corresponding output bit stream, representing the data read from the hard disk.
Unfortunately, the use of magneto-resistive read heads may alter the reading signal. Indeed, because of a phenomenon known as “magneto-resistive asymmetry”, the reading signal may feature second harmonic distortions, having an intensity that is proportional to the amplitude of the signal itself. Such second harmonic distortions may cause errors in the interpretation of the reading signal, such as to provoke the generation of a wrong output bit stream.
The characteristics of the second harmonic distortion due to the magneto-resistive asymmetry phenomenon depends on the type of read head used, and thus it is not foreseeable a priori. As a consequence, in order to be able to use magnetic-resistive read heads without causing an erroneous interpretation of the data read, it is desirable to be capable of eliminating, or at least reducing as much as possible, whichever second harmonic distortion's characteristics that may be present in the reading signal.
A possible solution is described in US 2002/0176197, which is incorporated by reference. Such document proposes a corrector circuit consisting of a pair of common-follower stages coupled with a differential load. The reduction of the second harmonic distortion is carried out by regulating the differential load, which is composed by two MOS transistors having different and programmable aspect ratios.